United Airlines CEO Oscar Munoz apologized again Tuesday for the carrier having police drag a passenger off a flight to make room for a crew member, but he didn't announce more policy changes during an earnings call beyond refunds and booking changes announced last week.

“This is a true learning opportunity and will ultimately prove to be a watershed moment for our company as we work harder than ever to put our customers at the center of everything that we do,” Munoz told investment analysts and reporters on the call. “We are and will make the necessary policy changes to make sure this never happens again.”

United’s internal investigation is scheduled to be completed with results reported by April 30. Munoz declined to say whether the airline would end overbooking sales, until the comprehensive review is completed.

"We are looking at a broad array of issues," Munoz said. "I would rather wait until we've the done the full work and we'll report on it next week."

President Scott Kirby said the company answered questions and concerns from corporate accounts, which are "largely supportive."

"We felt pretty good about the communications that we've had so far and our ability to reassure them and explain things like overbooking," Kirby said. "Some of the steps that we will do is brought to public on our April 30 launch."

Munoz said the failure was systemic, so the company didn't consider firing anyone in management or among rank-and-file workers.

“The buck stops here. I’m sure there was lots of conjecture about me personally," Munoz said. "It was a system failure across various areas. No, there was never a consideration for firing an employee or anyone around it."

Asked if there was a drop in bookings from China, where video of the incident provoked widespread outrage, President Scott Kirby said it's too early to say because there are too few days to measure possible changes. Munoz said he's met with the Chinese consulate to discuss the incident and has a previously planned trip to China within a few weeks.

"It's been a trip that was planned for some time," Munoz said of the trip to visit locations and customers.

Munoz had repeatedly apologized to the passenger, David Dao, other passengers on United Express Flight 3411 on April 9 and the rest of the airline's passengers.

“You can and should expect more from us, and as CEO I take full responsibility for making this right,” Munoz said.

Dao suffered a concussion, a broken nose and lost two teeth in the incident when Chicago aviation police dragged him off the flight, according to his lawyer, Thomas Demetrio. Three officers have been placed on administrative leave while the incident is investigated.

Dao was among four passengers removed from the sold-out flight to make room for airline crew members.

The airline has already offered refunds to passengers on the flight and said police will no longer be call police to remove paid, seated passengers from flights, unless for safety or security issues, Munoz said. The airline will also require that crews be booked on flights at least 60 minutes before departure.

“Our entire leadership team and the entire airline is focused on learning from this terrible event and making United truly customer focused on everything that we do,” Kirby said. “We’re committed to learning from last week’s failure.”